The microbe communities live on the undersides of rocks (green coloration)

It seems wherever scientists look on Earth they can usually find some kind of lifeform eking out an existence.

And microbe colonies discovered living under rocks in the Arctic and Antarctic are just the latest example.

Their high-latitude polar habitats are among the most extreme on the planet, with damaging levels of ultraviolet light as well as sub-zero temperatures.

These simple photosynthetic organisms, called cyanobacteria, are reported in the journal Nature by a UK/US team.

Charles Cockell, from the British Antarctic Survey, and Dale Stokes, from the US Scripps Institution of Oceanography, tell the magazine how they studied 850 dolomitic rocks.

Seasonal changes

The stones were chosen at random on Cornwallis Island and Devon Island in the Canadian High Arctic.

And although less than 1.2% of these polar areas are covered in vegetation, the scientists discovered that over 90% of the rocks they looked at were colonized by the cyanobacteria.

Similar activity was reported for stones at Mars Oasis on Alexander Island on the Antarctic Peninsula.

"Although it's not usual to find micro-organisms thriving under quartz and translucent rocks in hot deserts because enough light gets through, we wouldn't have expected this type of colonization in the polar regions where most of the rocks are opaque," says Dr Cockell.

"Also, the harsh UV-radiation and violent winds make for a hostile environment.

"We found that in fact the opaque rocks protect the micro-organisms and the movement of rocks during the annual freeze-thaw allows cracks to form and light to penetrate beneath the surface."

Life on Mars

The researchers describe this type of habitat as "hypolithic".

Their study suggests the productivity of this under-the-stones ecosystem is at least as great as that of above-ground organisms - the plants, lichens and mosses that dot the harsh landscape.

Devon Island: Not a place you would choose to live

It also underlines again the great adaptability of life. Scientists have found so-called extremophiles that can resist quite remarkable levels of radiation, acidity, alkalinity, salinity, and toxicity from heavy metals.

These discoveries encourage astrobiologists that similar micro-organisms will be found off Earth on other planets and moons in our Solar System.

"This shows us that places we may think of as extreme - for example other planets like Mars - could nurture surprising habitats for life," explains Dr Cockell.

"The Poles are not the barren wilderness, devoid of life as we previously thought".